Prions are infectious proteins that cause neurodegenerative diseases in humans and animals. Prions exhibit unusual resistance to inactivation by chemical and physical methods that generally destroy infectious pathogens such as bacteria, fungi, and viruses. Normal hospital sterilization procedures do not inactivate prions, leading to the possibility of iatrogenic prion disease. The studies proposed here on the inactivation of a range of prion strains should increase our knowledge of prions substantially. Previous studies showed that prions become protease-sensitive after exposure to branched polyamines in the presence of a weak acid. These findings have been extended to the study of denaturing detergents, including sodium dodecyl sulfate (SDS) in acidic solutions. We have determined that treatment with acidic SDS combined with autoclaving reduces the infectivity of Syrian hamster Sc237 and human sCJD prions by a factor of >106. Prion inactivation will be studied using prion-infected brain homogenates and prion-coated wires, which serve as a model for surface contamination. Employing a battery of biophysical strategies, we plan to define the mechanism of prion inactivation by acidic SDS. These investigations may decipher the structural features of prions that make some strains extremely resistant and others quite labile to inactivation. Initially, we plan to study three strains of prions passaged in mice: RML and 301V, which originated from sheep with scrapie and cattle with BSE, respectively, plus a novel synthetic strain MoSP1, which is the most stable strain reported to date. We will undertake a systematic study of human sCJD prions to define the spectrum of stabilities, and produce novel human synthetic prion strains to extend the range of samples tested. Furthermore, we will attempt to identify noncorrosive denaturants that are more efficacious than acidic SDS, and adjuncts to acidic SDS treatment such as hydrogen peroxide, which may be as effective at lower temperatures. Finally, we plan to develop methods that will reduce the duration required for bioassays. Recent studies demonstrated that mice lacking the protein interleukin-10 are more susceptible to prion disease;we will breed these mice with our transgenic lines in the hope of reducing the incubation period. We also plan to develop an in-vitro assay for prion infectivity using neurospheres prepared from transgenic mice. The results from the studies proposed here have a very high likelihood of adding substantially to our basic knowledge of prion biology and leading to the development of effective procedures for inactivating prions. Effective protocols for inactivating prions will protect the general public as well as laboratory scientists who are investigating prions. Rarely does a research study have such immediate and important implications.